Tin plating bath and method

ABSTRACT

An aqueous bath for electroplating tin upon various conductive substrates contains stannous ion, sulfate radical, an imidazoline derivative, a carbinamine compound, and a cyclic aldehyde or ketone brightener. The bath is highly acid and is operable to produce dense, smooth, bright, adherent deposits, particularly at relatively high current densities. These deposits exhibit excellent solderability as plated and after prolonged aging. In addition, the bath avoids step plating when holes are present in the workpiece, and it minimizes the tendency for pitting to occur in the deposit.

United States Patent Inventors Joseph F. Conoby Somers; Kenneth P. Belllnger, Rockville, both of Conn.

Appl. No. 878,221

Filed Nov. 19, 1969 Patented Oct. 26, 1971 Assignee Conversion Chemical Corporation Rockvllle, Conn.

TIN PLATING BATH AND METHOD 32 Claims, N0 Drawings US. Cl 204/54 R, 204/DIG. 2 Int. Cl C23!) 5/14, C23b 5/46 Field of Search 204/54 R,

54 L, 43,44,120, 123,DIG. 2; 106/1; 117/130 E [56] References Cited UNITED STATES PATENTS 3,361,652 1/1968 Korpiun et al. 204/54 R 3,429,790 2/1969 Schoot et a1. 204/54 R FOREIGN PATENTS 758,574 5/1967 Canada 204/54 Primary Examiner-G L. Kaplan Att0rney Peter L. Costas ABSTRACT: An aqueous bath for electroplating tin upon various conductive substrates contains stannous ion, sulfate radical, an imidazoline derivative, a carbinamine compound, and a cyclic aldehyde or ketone brightener. The bath is highly acid and is operable to produce dense, smooth, bright, adherent deposits, particularly at relatively high current densi ties. These deposits exhibit excellent solderability as plated and after prolonged aging. In addition, the bath avoids step plating when holes are present in the workpiece, and it minimizes the tendency for pitting to occur in the deposit.

TIN PLATING BATH AND METHOD BACKGROUND OF THE INVENTION A variety of baths have been employed for electrodepositing tin upon metallic substrates, possibly the most widely used of which are the stannous fluoborate and caustic stannate solutions. Although these prior art baths have proven generally satisfactory and have been widely utilized, they are usually deficient in one or more desirable operating characteristics, and the deposits which they produce frequently fail to provide a desirable balance of brightness, smoothness, ductility, adherence, solderability, porosity, uniformity and stability against aging. Some of the baths are relatively expensive and many tend to be difficult to maintain since fairly critical control of the concentrations of the components thereof is normally required. Recent efforts to provide bright tin deposits are described by P. Baeyens and G. Krijl in Philips Formaldehyde Bright Tin", in TRANSACTIONS OF THE IN- STITUTE OF METAL FINISHING,1967, Vol. 45, at Pages 115-121, and in Korpiun et al. U.S. letters Pat. No. 3,361,562.

In the literature and in patents are described various baths which are operable with varying degrees of efficiency and effectiveness. Excellent deposits are produced under most circumstances by the acid tin sulfate electroplating compositions described in two copending applications for U.S. letters Pat.; i.e., applicants Ser. No. 768,181 entitled Method and Composition for Electroplating Tin", and Rynne and Beckwith Ser. No. 774,177, entitled Method and Bath for Electroplating Tin, which are assigned to the assignee of the present invention. Nevertheless, there remains a need for a bath capable of producing smooth, bright, dense, adherent deposits which exhibit desirable soldering properties, which resist aging, and.

which avoid step plating when holes are present in the workpiece.

Accordingly, it is an object of the present invention to provide a bath for producing smooth, adherent, dense, bright and relatively nonporous deposits of tin.

It is also an object to provide such a bath which minimizes pitting, avoids step plating about holes in the workpiece, and which produces relatively smooth deposits upon relatively rough surfaces.

Another object is to provide a bath capable of producing a deposit that exhibits high corrosion protection and excellent solderability, both as plated and after prolonged aging, which also does not tarnish and is highly resistant to staining.

Still another object is to provide such a bath for electrodepositing tin at suitable operating rates and which does not require a high level of control of the concentration of the components thereof within critical limits.

A further specific objectis to provide a convenient and relatively rapid method for electroplating tin upon metallic workpieces utilizing an improved sulfate plating bath to obtain highly desirable tin deposits at relatively low cost.

SUMMARY OF THE INVENTION It has now been found that the foregoing and related objects can be readily attained in an aqueous bath comprising about 35.0 to 85.0 grams per liter of stannous ion, about 70.0 to 250.0 grams per liter of sulfate radical; about 0.25 to 25.0 grams per liter of a surface active imidazoline derivative, 0.0 to about 5.0 grams per liter of a condensate of an alkylphenol having an alkyl chain of six to 12 carbon atoms with an alkylene oxide selected from the class consisting of ethylene oxide, propylene oxide, and mixtures thereof, about 0.15 to 15.0 grams per liter of a ten-carbinamine polyoxyalkylene compound, about 0.005 to 1.0 gram per liter of a brightener selected from the group consisting of cyclic ketones, cyclic aldehydes and mixtures thereof, and about 0.9 to 4.5 grams per liter of hydrogen ion. The carbinamine compound has the wherein R,, R and R are alkyl groups which together contain seven to 23 carbon atoms and X is selected from the class consisting of -H and the group 'When X is -H, a represents an integer from 15 to 45, b

represents a number from 15 to 67.5 and the ratio bza has a value of 1.01.5:l.0. When X is the group defined, a+c represents an integer from 15 to 45, b+d represents a number from 15 to 67.5 and the ratio (b+d):(a+c) has a value of 1.0-1.51.0.

The preferred bath comprises about 55.0 to 75.0 grams per liter of stannous ion, about 125.0 to 200.0 grams per liter of sulfate radical, about 1.0 to 15.0 grams per liter of the imidazoline derivative, about 0.1 to 1.0 gram per liter of the alkylphenol condensate, about 0.5 to 10.0 grams per liter of the carbinamine compound, about 0.05 to 0.5 gram per liter of the brightener and about 1.5 to 3.0 grams per liter of hydrogen ion. Most desirably, the imidazoline derivative and the carbinamine compound are present in concentrations of about 5.0 to 10.0 and about 2.0 to 5.0 grams per liter, respectively.

In accordance with the electroplating method of the invention an aqueous acid bath having the composition previously defined is first prepared and maintained at a temperature of about 45 to 135. A workpiece having a metallic surface and a tin anode are immersed in the bath, and a voltage is applied thereacross to deposit tin on the metallic surface, the voltage providing a current density of about 10.0 to 200.0 amperes per square foot at the workpiece. In the preferred method, the bath is maintained at a temperature of about 60 to Fahrenheit and the voltage provides a current density of about 50.0 to 100.0 amperes per square foot at the workpiece. Most desirably, the ratio of the area of the anode to that of the workpiece is about 1.5 to 3.0:1.0, and the current density at the anode is less than about 40.0 amperes per square foot.

DESCRIPTION OF THE PREFERRED EMBODIMENTS For proper operation, the acid baths of the present invention require the stannous ion, the sulfate radical, an imidazoline derivative, a carbinamine polyoxyalkylene compound, and a cyclic aldehyde or ketone brightener. The stannous ion and the sulfate radical may be furnished to the bath by any combination of compounds suitable for use in tin plating solutions, but, to avoid the presence of unnecessary and possibly interfering ions, these components are desirably introduced percent the form of stannous sulfate and sulfuric acid. As is apparent, the former compound will provide both the stannous ion and the sulfate radical, whereas the latter compound provides additional sulfate radical which is present in the bath. The use of sulfuric acid is also desirable from the standpoint of control of the hydrogen ion concentration, although other acids providing noninterfering radicals may also be used for that purpose. Less desirably, tin compounds other than stannous sulfate, e.g., stannous fluoborate, may be employed; when used, they are preferably present in concentrations of not more than about 50.0 percent by weight of the sulfate compound, and more preferably they provide less than 20.0 percent by weight thereof.

Although the amount of stannous ion present in the baths may vary between about 35.0 and 85.0 grams per liter, it is preferably about 55.0 to 75.0 grams per liter. Similarly, although the concentration of sulfate ion may normally be between about 70.0 and 250.0, it is preferably about 125.0 to 200.0 grams per liter. A broad range of about 0.9 to 4.5 grams per liter is suitable for the hydrogen ion concentration, however, it is most desirably maintained at about 1.5 to 3.0 grams per liter. If the concentration of stannous ion in the bath is too low, the efficiency of plating and the quality of the deposit produced will be unsatisfactory at low current densities, and burning willbe apparent at the high end of the current density range. On the other hand, although desirable deposits are obtained at higher current densities with relatively high concentrations of stannous ion, too great an amount will tend to produce a very poor deposit at low current densities and to adversely affect brightness and other qualities of the deposit. Maintaining the sulfate radical and the hydrogen ion within the ranges of concentrations specified will ensure that the bath operates efficiently to produce the quality of deposit desired.

THE SURF ACE-ACTIVE AGENTS In addition to the stannous ion and sulfate radical, the acid baths of the present invention require effective amounts of an imidazoline derivative and of a carbinamine compound, and preferably but optionally they may contain a condensate of an alkyl phenol with an alkylene oxide. The imidazoline derivative corresponds to the formula:

1120-011, omz

wi omomy N=C o In the foregoing formula, R represents an alkyl radical having five to 24 carbon atoms; 6 is the -OH ion, an acid salt radical, an anionic surface-active sulfate salt radical such as preferably -OSO -OR, or an anionic surface-active sulfonate salt radical; and Z is -COOM, -CH COOM, or -CHOH-CH SO:,M radical. The substituent designated M in the foregoing formula is a hydrogen atom, an alkali metal or an organic base, and that designated Y is either an -OR or -N(R) A group. Each R substituent is independently selected from the group consisting of hydrogen, alkali metals, and -(CH ),,COOM; A

represents an anionic monovalent radical and n represents an integer from 1 to 4. Use of the dotted line representation for the bonds connecting the substituents G and CH Z to the nitrogen atom indicates that these substituents are optionally present or absent, but it should be understood that they are either both present or both absent. Desirable compounds are provided when, in accordance with the foregoing formula, G represents the radical -OSO -OR, particularly in which R is a C to C alkyl group, and Z is a -COOM radical in which M is preferably an alkali metal cation.

Exemplary of the compounds corresponding to the foregoing formula which are satisfactory for use in the baths described herein are 2-alkyl-l-(ethyl-beta-oxypropanoic acid) imidazolines wherein the alkyl group is capryl, undecyl or a mixture of C -C chains, and the disodium salt of lauroylcycloimidinium-l-ethoxyethanoic acid-2-ethanoic acid. Moreover, it may be found that the best results are obtained by using combinations of the imidazoline derivatives. Particularly significant benefits may be obtained with a mixture of (A) an imidazoline derivative wherein the groups -G and CH Z are both omitted and Y is -N[(CH ),,-COOH] C1, n being equal to 1 to 4; and (B) an imidazoline derivative wherein -G is -OH and wherein -Y is equal to -O(CH ),,COOM and wherein Z is equal to -(CH ),,,COOM, n being equal to l to 4 and m equal to to l and M being an alkali metal. A second beneficial system may be a mixture of an imidazoline corresponding to the aforementioned general formula wherein Z is COONa, -G is OH, and Y is OCH COONa; and a second imidazoline wherein the groups G and -CH Z are omitted and Y is -N(CH CH COOH) (CH COOH)CI. The first-mentioned imidazoline derivative is provided in a weight ratio of about 1 to 8:1 relative to the second-mentioned imidazoline derivative and preferably in a ratio of about 4.5 to 6.5.

The carbinamine compound employed is that which has hereinbefore been presented and defined. Preferably, however, it has the general formula wherein e is an integer from 12 to 15; most desirably, X is -H and a and b each represent numbers from 15 to 20. The carbinamine compounds are described in Boettner et al. U.S. Pat. No. 3,117,999, granted on Jan. 4, 1964. For effective results, the carbinamine compound (or mixture thereof) should be used in a concentration of about 0.15 to 15.0 grams per liter. Preferably, the amount thereof is about 0.5 to 10.0 grams per liter, and most desirably it is about 2.0 to 5.0 grams per liter.

Although the carbinamine compound and the imidazoline derivative are generally adequate, as the only surface-active agents, to attain the objects of the present invention, most often the best deposits will be produced by use of the combination along with the alkylphenol/alkylene oxide condensate. The alkylene oxide will be present in a molar ratio relative to the alkyl phenol of about 8.0 to 25.0:l.O, and is selected from the class consisting of ethylene oxide, propylene oxide and mixtures thereof. The alkyl substituent of the phenol has a carbon chain of six to 12 carbon atoms and preferably eight to 10. Exemplary of the alkyl phenol condensates are octyl phenoxy polyethoxy ethanols and nonyl phenoxy polyethoxy ethanols, with the preferred agents being nonyl phenoxy polyethoxy ethanols having an oxidezphenol molar ratio of about 19.0 to 20.0: 1 .0.

THE CYCLIC BRIGHTENERS The remaining essential component of the bath is a brightener selected from the group consisting of cyclic aldehydes, cyclic ketones and mixtures thereof. Any suitable compounds of these types may be employed, and the carbonyl group may be attached directly to the ring or connected through one or more atoms. Specific examples of the cyclic ketones that may be appropriate in a particular bath are benzylideneacetone, methyl phenyl ketone, isopropyl phenyl ketone, 4-(2-furyl)-3-butene-2-one, 4-p-sulfophenyl-3-butene-Z-one, 1,5-di-p-sulfophenyl-l,4-pentadiene-3-one, 4- hydroxy-3-methoxy-benzylideneacetone, 4-(pyridyl-2)-3-butene-Z-one, furylideneacetone, pyridylideneacetone, etc. Exemplary of the cyclic aldehydes that are suitable as brighteners are 2-pentyl-3-phenyl-propenal, o-anisaldehyde, p-anisic aldehyde bisulfite, furfural, glutaraldehyde, cinnamaldehyde, veratraldehyde, benzaldehyde, o-chlorobenzaldehyde and p-chlorobenzaldehyde. Preferably, the aldehyde has a five-membered heterocyclic ring, and most desirably the aldehyde group is attached to one of the carbons in the ring, which generally will be that in the two-position. Although longer carbon chain aldehydes may be used, the particularly preferred compounds are those which contain a simple aldehyde group (-CHO), and the aldehydes may be ring or chain substituted. Particularly good results are attained by the use of aldehydes based upon thiophene, furan and pyrrole, and specific heterocyclic carboxaldehydes which have proven highly effective are furfural (Z-furaldehyde), Z-thiophene carboxaldehyde and 2-pyrrole carboxaldehyde.

Although beneficial results have been obtained by the incorporation of the brightener in amounts of as little as 0.0005 gram per liter, it is preferably included in amounts of at least about 0.05 gram per liter. As the concentration of brightener is increased above about 0.5 gram per liter, it becomes increasingly difficult to control operation of the bath, and above about 1.0 gram per liter pitting and burning become quite evident and the level of brightness at low current densities is diminished significantly. Accordingly, the baths preferably employ the aldehyde or ketone compounds in amounts of about 0.05 to 0.5 gram per liter.

Since some of the suitable brighteners demonstrate relatively low solubility in the acid bath, it may be necessary to em ploy a solvent solution thereof to facilitate formulation of the bath. Among the various solvents which may be employed, depending upon the particular brightener involved, are the low molecular weight alkanols (methanol, ethanol and propanol) and the low molecular weight glycol ethers (ethylene glycol monoethyl ether, etc.). Generally, the brightener is added to the solvent in amounts of about 1.0 to 50.0, and preferably in about 5.0 to 25.0 grams per liter thereof, so as to obtain a stable solvent solution which may be readily dispersed in the acid bath.

OTHER COMPONENTS Although it has generally been found that the bath desirably operates without additional components, other additives may be included to modify the operation of the present bath, such as surface-active agents, chelating agents and auxiliary brighteners. Exemplary of such auxiliary brighteners are the polyvinyl alcohols which should usually be added in amounts of less than 1.0 gram per liter and preferably less than 0.2 gram per liter. Although little or no tendency for metal sludge and precipitate formation has been noted in properly operated baths, for some applications it may be desirable to incorporate a chelating agent such as citric acid, malic acid and the aminopolyacetic acids, e.g., ethylene-diamine tetraacetic acid, diethylene-triamine pentaacetic acid, and nitrilotriacetic acid. Such chelating agents, when employed, are generally included in an amount of5.0 to 20.0 grams per liter.

OPERATION OF THE BATHS As has been indicated previously, the baths of the present invention are operable over a fairly wide range of cathode current density, depending upon other factors such as temperature, agitation, etc. More specifically, the operable range is about 10.0 to 200.0 amperes per square foot (ASF) and preferably about 25.0 to 150.0 ASF, with a narrower range of 50.0 to 100.0 ASF being most desirable. The plating efficiency is generally quite high and will range up to about 95 percent under optimum conditions, based upon the theoretical rate of deposition, and bright deposits of excellent quality can normally be produced at a bath efficiency in excess of 70 percent. In order to obtain optimum results, the anodezcathode ratio should be about 1.5 to 3.0:l.0, and preferably about :10 Moreover, the anode current density should not exceed about 40 ASF since there is an apparent tendency for inefficient operation, excessive sludging and rough deposits to be formed at higher anode current densities. The applied voltage should be about 0.2 to 5.0 volts and preferably 0.5 to 4.0 volts.

The baths should be operated at temperatures between about 45 and 135 Fahrenheit, and preferably about 60 to 90 Fahrenheit. Operation below about 45 Fahrenheit tends to be inefficient and to produce undesirable deposits, whereas temperatures higher than about 135 Fahrenheit tend to produce dull, rough and generally unacceptable deposits, and the bath is consumed at an excessive rate.

Any metallic substrate or metal-surfaced article which can be plated with tin using prior art baths may be coated in accordance with the present invention. For example, good deposits of tin may be produced upon articles of copper, nickel, iron, steel, etc. The best results are obtainable with these baths if relatively pure tin anodes are employed, but alloy anodes may also be feasible.

Agitation is highly desirable to obtain high quality, uniform deposits and to avoid development of sludge or film, and plating at high current densities and temperatures is improved by more intense agitation. However, excessively high rates of agitation are undesirable because they can cause excessive consumption of the bath and impose limitations upon the current densities at which brightness is achieved. Not only is agitation of the bath itself desirable but agitation of the cathode may be beneficial in obtaining a uniform plate and enabling extension of the range of satisfactory current density.

The process is adapted to still plating and barrel plating apparatus with equal efficacy, and may be used for strip, wire and connector strip. Use of the bath and process is particularly significant with respect to connector strip and the like because of the excellent solderability of the plate produced and the avoidance of step plating (i.e., due to upsetting of polarization) thereby. Filtration of the bath is not essential but will normally be beneficial when contamination of the bath is encountered due to airborne impurities and carryover from other finishing operations; preferably, it will be effected on a continuous basis. Various filtering media may be utilized including fabric, porous stoneware and other conventional filtering materials.

The depletion of the various components of the bath is best corrected by analysis for the several components on a periodic basis which can be established for a given facility. To determine the necessity for the addition of a surface-active agent, the best procedure is to evaluate a sample of the bath in a suitable test cell, and a suitable schedule may be established for a given facility and workpiece. To determine the amounts of stannous salt required, a 0.1 N potassium iodate solution and a 1.0 percent solution of starch may be used for titration. The free sulfuric acid concentration may be determined by simple titration procedures with a suitable indicator such as thymophtalein. The amount of brightener required is best evaluated by testing a sample of the bath in a suitable test cell.

Illustrative of the efficacy of the present invention are the following specific examples wherein all parts are parts by weight unless otherwise indicated.

EXAMPLE ONE An aqueous bath is prepared containing 120.0 grams per liter of stannous sulfate, 92.0 grams per liter of sulfuric acid; 4.5 grams per liter of a commercial imidazoline derivative wherein groups -G and -CH,Z are omitted and Y is N(CH CH COOH) (CH COOH)Cl; 0.75 gram per liter of a second commercial imidazoline derivative wherein Z is COONa, -G is -OH, and -Y is OCH COONa; 0.93 gram per liter of an ethylene oxide/octyl phenol condensate having a molar ratio of about 10.0:l.0; 4.1 grams per liter ofa commercial mixture of carbinamine compounds having the formula t- C,H ,,+,NH(C H,O),,(C;,H O),,H, wherein e is an integer from 12 to 15 and a and h each represent numbers 15 to 20; and 0.08 gram per liter of thiophene aldehyde. The bath is introduced into strip plating apparatus and maintained at a temperature ofabout 68 Fahrenheit.

Into the bath is introduced a punched steel connector strip and a pure tin anode. A potential of about 3 volts is impressed across the strip and the anode, providing a current density at the cathode of about ASF and at the anode of less than 40 ASF. The strip is agitated and plated for a period of about 2 minutes in the bath. Upon inspection of the strip after removal from the bath, rinsing and drying, a bright, dense, adherent deposit of tin is found to be present, which deposit is smooth and free of pitting and is uniform throughout, even about the holes. Solderability as plated and after prolonged aging is found to be excellent.

EXAMPLE TWO A tin solution is prepared by dissolving in water 132.0 grams per liter of stannous sulfate, 55.0 milliliters per liter of sulfuric acid and about 0.1 gram per liter of thiophene aldehyde. A first aqueous stock solution (designated A) is prepared by admixing the octylphenol condensate and the imidazoline derivative first mentioned in example one, in concentrations of 20.0 and 80.0 grams per liter, respectively. A second stock solution (designated B) is prepared by dissolving in water 100.0 grams per liter ofthe same mixture of carbinamine compounds as is used in that example. A series of tests is run using steel panels in Hull cells which contain baths formed from different proportions of the three solutions. The baths are operated at 75 Fahrenheit with 5 amperes applied for 3 minutes; agitation is provided by a stirring rod moved across the face of the panel. Set forth in the following table are the volumes of the stock solutions in the several baths, the bright plating range (in amperes per square foot) and a visual description of the deposit produced.

TABLE ONE Tin Bright solution, Solution Solution rang Test N parts "11, parts B, parts (ASF) Description of deposit 250 12 2% 20-200 Cloudy bright. 250 12 5 30-200 Cloudy bright-better than No. 1. 250 12 20-150 Bright. 250 12 20 20-200 Cloudy bright. 250 24 5 20-150 ery bright. 250 24 10 20-200 D0. 250 24 20 20-175 Do.

Thus, it can be seen that the present invention provides a bath and method for producing a smooth, adherent, dense, bright and relatively nonporous deposit of tin; pitting is minimized, step plating about holes in the workpiece is avoided and relatively smooth deposits may be produced upon relatively rough surfaces. There is no need for a high level of control of the concentration of the components of the bath within critical limits, and the bath is capable of producing a deposit that does not tarnish, is highly resistant to staining, and that exhibits high corrosion protection and excellent solderability, both as plated and after prolonged aging.

Having thus described the invention, we claim:

1. An aqueous acid bath for producing an adherent electroplated tin deposit comprising about 35.0 to 85.0 grams per liter of stannous ion; about 70.0 to 250.0 grams per liter of sulfate radical; about 0.25 to 25.0 grams per liter of a surface active imidazoline derivative; 0.0 to about 5.0 grams per liter of a condensate of an alkylphenol having an alkyl chain of six to 12 carbon atoms with an alkylene oxide selected from the class consisting of ethylene oxide, propylene oxide and mixtures thereof; about 0.15 to 15.0 grams per liter of a tert.-carbinamine polyoxyalkylene compound having the general formula:

wherein R,, R and R are alkyl groups which together contain seven to 23 carbon atoms and X is selected from the class consisting of-H and the group a representing an integer from to 45, b representing a number from 15 to 67.5 and the ratio b:a having a value of 1.0-1.51.0 when X is -H, and a+c representing an integer from 15 to 45, b+d representing a number from 15 to 67.5 and the ratio (b+d):(a+c) having a value of l.0-l.5:l.0 when X is said group; about 0.005 to 1.0 gram per liter of a brightener selected from the group consisting of cyclic aldehydes, cyclic ketones and mixtures thereof; and about 0.9 to 4.5 grams per liter of hydrogen ion.

2. The bath of claim 1 comprising about 55.0 to 75.0 grams per liter of stannous ion; about 125.0 to 200.0 grams per liter of sulfate radical; about 1.0 to 15.0 grams per liter of imidazoline derivative; about 0.1 to 1.0 gram per liter of alkyl phenol condensate; about 0.5 to 10.0 grams per liter of carbinamine compound; about 0.05 to 0.5 gram per liter of brightener; and about 1.5 to 3.0 grams per liter of hydrogen ion.

3. The bath of claim 2 wherein said imidazoline derivative and said carbinamine compound are present in respective concentrations of about 5.0 to 10.0 grams per liter and about 2.0 to 5.0 grams per liter.

4. The bath of claim 1 wherein the imidazoline derivative corresponds to the formula:

wherein:

l. R is an alkyl radical having five to 24 carbon atoms; 2. G is a radical selected from the group consisting of -OH,

acid salt radicals, anionic surface active sulfate salt radicals, and anionic surface active sulfonate salt radicals;

3. Z is a radical selected from the group consisting of COOM, -CH COOM, and -CHOH-CH SO M;

4. M is a substituent selected from the group consisting of hydrogen, alkali metals and organic bases;

5. Y is selected from the group consisting of -OR and 6. each R substituent is independently selected from the group consisting of hydrogen, alkali metals, and -(CH COOM;

7. A is an anionic monovalent radical;

8. n is an integer from 1 to 4; and

9. both the groups G and CH Z are present or absent.

5. The bath of claim 4 wherein said imidazoline derivative has a structure wherein -G is an anionic surface active sulfate salt radical having the formula -OSO -OR in which sulfate salt radical R is an alkyl group containing 10 to 18 carbon atoms,

and wherein Z is a -CO0M radical in which M is an alkali metal cation.

6. The bath of claim 1 wherein said imidazoline derivative is selected from the group consisting of 2-alkyl-l-(ethyl-betaoxypropanoic acid)-imidazolines wherein the alkyl group is selected from the class consisting of capryl, undecyl and mixtures of C -C chains, and the disodium salt of lauroyl-cycloimidinium-l-ethoxy-ethan0ic acid-Z-ethanoic acid.

7. The bath of claim 1 wherein said imidazoline derivative is a mixture of (A) an imidazoline derivative wherein the groups -G and -Cl-1 Z are both omitted and Y is -N[(CH COOHhCl n being equal to l to 4; and (B) an imidazoline derivative wherein -G is -OH, wherein -Y is equal to O(CH ),,COOM and wherein Z is equal to -(CH ),,,COOM, n being equal to 1 to 4 and m equal to 0 to I, and M being an alkali metal.

8. The bath of claim 7 wherein imidazoline derivative (A) is present in a weight ratio relative to imidazoline derivative (B) ofabout 1.0 to 8.0:1 .0.

9. The bath of claim 1 wherein the alkyl group of said alkyl phenol in said condensate is selected from the class consisting of octyl, nonyl and mixtures thereof.

10. The bath of claim 1 wherein said carbinamine compound has the general formula and wherein e is an integer from 12 to 15.

11. The bath of claim 10 wherein in said carbinamine compound X is -H and a and h each represent numbers from 15 to 20.

12. The bath of claim 1 wherein said brightener has a heterocyclic ring and wherein an aldehyde group is attached directly to a carbon atom in the ring.

13. The bath of claim 12 wherein said heterocyclic ring contains five members.

14. The bath of claim 13 wherein said aldehyde brightener is thiophene aldehyde.

15. The bath of claim 1 wherein at least the predominant portion of said stannous ion is provided by stannous sulfate and wherein a portion of said sulfate radical is furnished by sulfuric acid.

16. In a method for electroplating tin, the steps comprising:

1. preparing an aqueous acid bath comprising about 35.0 to

85.0 grams per liter of stannous ion; about 0.25 to 25.0 grams per liter of a surface active imidazoline derivative; 0 to about 5.0 grams per liter of a condensate of an alkyl phenol having an alkyl chain of six to 12 carbon atoms with an alkylene oxide selected from the class consisting of ethylene oxide, propylene oxide;v about 0.15 to 15.0 grams per liter of a tert.-carbinamine polyoxyalkylene compound having the general formula:

wherein R,, R and R are alkyl groups which together contain seven to 23 carbon atoms and X is selected from the class consisting of -l-l and the group a representing an integer from 15 to 45, b representing a number from 15 to 67.5 and the ratio bza having a value of l.01.5:1.0 when X is l-l, and n+0 representing an integer from 15 to 45, Irl-d representing a number from 15 to 67.5 and the ratio (lH-d):(a+c) having a value of 1.0-1.51.0 when X is said group; 0005 to 1.0 gram per liter of a brightener selected from the group consisting of cyclic aldehydes, cyclic ketones, and mixtures thereof; and about 0.9 to 4.5 grams per liter of hydrogen ion; 2. maintaining said bath at a temperature of about 45 to 135 Fahrenheit; immersing a workpiece having a metallic surface and a tin anode in said bath; and 4. applying a voltage across said anode and workpiece to deposit tin on said metallic surface, said voltage providing a current density of about 10.0 to 200.0 amperes per square foot at the workpiece 17. The method of claim 16 wherein said bath is maintained at a temperature of about 60 to 90 Fahrenheit and wherein said voltage provides a current density of about 50 to 100 amperes per square foot at the workpiece.

18. The method of claim 17 wherein the ratio of the area of said anode to that of the workpiece is about 1.5 to 3.011 .0, and wherein the current density at said anode is less than about 40 amperes per square foot.

19. The method of claim 16 comprising about 55.0 to 75.0 grams per liter of stannous ion; about 125.0 to 200.0 grams per liter of sulfate radical; about 1.0 to 15.0 grams per liter of imidazoline derivative; about 0.1 to 1.0 gram per liter of alkyl phenol condensate; about 0.5 to 10.0 grams per liter of carbinamine compound; about 0.05 to 0.5 gram per liter of brightener; and about 1.5 to 3.0 grams per liter of hydrogen ion. a

20. The method of claim 19 wherein said imidazoline derivative and said carbinamine compound are present in respective concentrations of about 5.0 to 10.0 grams per liter and about 2.0 to 5.0 grams per liter.

21. The method of claim 16 wherein the imidazoline derivative corresponds to the formula:

wherein:

l. R is an alkyl radical having tive to 24 carbon atoms; 2. G is a radical selected from the group consisting of -OH,

acid salt radicals, anionic surface active sulfate salt radicals, and anionic surface active sulfonate salt radicals;

3. Z is a radical selected from the group consisting of COOM, -CH CO0M, and -CHOH-Cl-l,SO M;

4. M is a substituent selected from the group consisting of hydrogen, alkali metals and organic bases;

5. Y is selected from the group consisting of -OR' and 6. eachrR' substituent is independently selected from the group consisting of hydrogen, alkali metals, and -(CH COOM; 7. A is an anionic monovalent radical;

8. n is an integer from 1 to 4; and

9. both the groups G and CH Z are present or absent.

22. The method of claim 21 wherein said imidazoline derivative has a structure wherein -G is an anionic surface-active sulfate salt radical having the formula -OSO -OR in which sulfate salt radical R is an alkyl group containing 10 to 18 carbon atoms, and wherein Z is a -COOM radical in which M is an alkali metal cation.

23. The method of claim 16 wherein said imidazoline derivative is selected from the group consisting of 2-alkyl-l- (ethyl-betaoxypropanoic acid)-imidazolines wherein the alkyl group is selected from the class consisting of capryl, undecyl and mixtures of C chains, and the disodium salt of lauroylcyclo-imidinium-l-ethoxyethanoic acid-Z-ethanoic acid.

24. The method of claim 16 wherein said imidazoline derivative is a mixture of (A) an imidazoline derivative wherein the groups -G and -CH Z are both omitted and Y is N[(CH )-COOH] -,C1, n being equal to l to 4; and (B) an imidazoline derivative wherein -G is -OH, wherein -Y is equal to -O(CH ),,COOM and wherein Z is equal to -(CH ),,,COOM, n being equal to l to 4 and m equal to 0 to l, and M being an alkali metal.

25. The method of claim 24 wherein imidazoline derivative (A) is present in a weight ratio relative to imidazoline deriva' tive (B) ofabout 1.0 to 8.0: l .0.

26. The method of claim 16 wherein the alkyl group of said alkyl phenol in said condensate is selected from the class consisting of octyl, nonyl and mixtures thereof.

27. The method of claim 16 wherein said carbinamine compound has the general formula and wherein e is an integer from 12 to 15.

28. The method of claim 27 wherein in said carbinamine compound X is -H and a and b each represent numbers from 15 to 20.

29. The method of claim 16 wherein said brightener has a heterocyclic ring and wherein an aldehyde group is attached directly to a carbon atom in the ring.

30. The method of claim 29 wherein said heterocyclic ring contains five members.

31. The method of claim 30 wherein said aldehyde brightener is thiophene aldehyde.

32. The method of claim 16 wherein at least the predominant portion of said stannous ion is provided by stannous sulfate and wherein a portion of said sulfate radical is furnished by sulfuric acid.

CERTIFICATE OF CORRECTION Patent No. 3, 616, 306 Dated March 15, 1972 Inventor(s) Joseph F. Conoby and Kenneth P. Bellinger It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Claim 16 line 74, after "stannous ion;" insert --about '70. 0 to 250. 0 grams per liter of sulfate radica1;--; line 2, after "propylene oxide", insert and mixtures thereof--;

line 20, after "group;" insert -about--.

Claim 7 line 35, delete the numeral '1" and substitute therefor the numeral --4--.

Claim 24 line 27, delete the numeral "16" and substitute therefor the numeral --21--.

Signed and sealed this 18th day of July 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

2. G is a radical selected from the group consisting of -OH, acid salt radicals, anionic surface active sulfate salt radicals, and anionic surface active sulfonate salt radicals;
 2. G is a radical selected from the group consisting of -OH, acid salt radicals, anionic surface active sulfate salt radicals, and anionic surface active sulfonate salt radicals;
 2. maintaining said bath at a temperature of about 45* to 135* Fahrenheit;
 2. The bath of claim 1 comprising about 55.0 to 75.0 grams per liter of stannous ion; about 125.0 to 200.0 grams per liter of sulfate radical; about 1.0 to 15.0 grams per liter of imidazoline derivative; about 0.1 to 1.0 gram per liter of alkyl phenol condensate; about 0.5 to 10.0 grams per liter of carbinamine compound; about 0.05 to 0.5 gram per liter of brightener; and about 1.5 to 3.0 grams per liter of hydrogen ion.
 3. The bath of claim 2 wherein said imidazoline derivative and said carbinamine compound are present in respective concentrations of about 5.0 to 10.0 grams per liter and about 2.0 to 5.0 grams per liter.
 3. immersing a workpiece having a metallic surface and a tin anode in said bath; and
 3. Z is a radical selected from the group consisting of -COOM, -CH2COOM, and -CHOH-CH2SO3M;
 3. Z is a radical selected from the group consisting of -COOM, -CH2COOM, and -CHOH-CH2SO3M;
 4. M is a substituent selected from the group consisting of hydrogen, alkali metals and organic bases;
 4. M is a substituent selected from the group consisting of hydrogen, alkali metals and organic bases;
 4. applying a voltage across said anode and workpiece to deposit tin on said metallic surface, said voltage providing a current density of about 10.0 to 200.0 amperes per square foot at the workpiece.
 4. The bath of claim 1 wherein the imidazoline derivative corresponds to the formula:
 5. Y is selected from the group consisting of -OR'' and -N(R'')3A;
 5. Y is selected from the group consisting of -OR'' and -N(R'')3A;
 5. The bath of claim 4 wherein said imidazoline derivative has a structure wherein -G is an anionic surface active sulfate salt radical having the formula -OSO2-OR in which sulfate salt radical R is an alkyl group containing 10 to 18 carbon atoms, and wherein Z is a -COOM radical in which M is an alkali metal cation.
 6. The bath of claim 1 wherein said imidazoline derivative is selected from the group consisting of 2-alkyl-1-(ethyl-betaoxypropanoic acid)-imidazolines wherein the alkyl group is selected from the class consisting of capryl, undecyl and mixtures of C7-C17 chains, and the disodium salt of lauroyl-cyclo-imidinium-1-ethoxy-ethanoic acid-2-ethanoic acid.
 6. each R'' substituent is independently selected from the group consisting of hydrogen, alkali metals, and -(CH2)n-COOM;
 6. each R'' substituent is independently selected from the group consisting of hydrogen, alkali metals, and -(CH2)n-COOM;
 7. A is an anionic monovalent radical;
 7. A is an anionic monovalent radical;
 7. The bath of claim 1 wherein said imidazoline derivative is a mixture of (A) an imidazoline derivative wherein the groups -G and -CH2Z are both omitted and Y is -N((CH2)n-COOH)3C1, n being equal to 1 to 4; and (B) an imidazoline derivative wherein -G is -OH, wherein -Y is equal to -O(CH2)nCOOM and wherein Z is equal to -(CH2)mCOOM, n being equal to 1 to 4 and m equal to 0 to 1, and M being an alkali metal.
 8. The bath of claim 7 wherein imidazoline derivative (A) is present in a weight ratio relative to imidazoline derivative (B) of about 1.0 to 8.0:1.0.
 8. n is an integer from 1 to 4; and
 8. n is an integer from 1 to 4; and
 9. both the groups G and CH2Z are present or absent.
 9. both the groups G and CH2Z are present or absent.
 9. The bath of claim 1 wherein the alkyl group of said alkyl phenol in said condensate is selected from the class consisting of octyl, nonyl and mixtures thereof.
 10. The bath of claim 1 wherein said carbinamine compound has the general formula and wherein e is an integer from 12 to
 15. 11. The bath of claim 10 wherein in said carbinamine compound X is -H and a and b each represent numbers from 15 to
 20. 12. The bath of claim 1 wherein said brightener has a heterocyclic ring and wherein an aldehyde group is attached directly to a carbon atom in the ring.
 13. The bath of claim 12 wherein said heterocyclic ring contains five members.
 14. The bath of claim 13 wherein said aldehyde brightener is thiophene aldehyde.
 15. The bath of claim 1 wherein at least the predominant portion of said stannous ion is provided by stannous sulfate and wherein a portion of said sulfate radical is furnished by sulfuric acid.
 16. In a method for electroplating tin, the steps comprising:
 17. The method of claim 16 wherein said bath is maintained at a temperature of about 60* to 90* Fahrenheit and wherein said voltage provides a current density of about 50 to 100 amperes per square foot at the workpiece.
 18. The method of claim 17 wherein the ratio of the area of said anode to that of the workpiece is about 1.5 to 3.0:1.0, and wherein the current density at said anode is less than about 40 amperes per square foot.
 19. The method of claim 16 comprising about 55.0 to 75.0 grams per liter of stannous ion; about 125.0 to 200.0 grams per liter of sulfate radical; about 1.0 to 15.0 grams per liter of imidazoline derivative; about 0.1 to 1.0 gram per liter of alkyl phenol condensate; about 0.5 to 10.0 grams per liter of carbinamine compound; about 0.05 to 0.5 gram per liter of brightener; and about 1.5 to 3.0 grams per liter of hydrogen ion.
 20. The method of claim 19 wherein said imidazoline derivative and said carbinamine compound are present in respective concentrations of about 5.0 to 10.0 grams per liter and about 2.0 to 5.0 grams per liter.
 21. The method of claim 16 wherein the imidazoline derivative corresponds to the formula:
 22. The method of claim 21 wherein said imidazoline derivative has a structure wherein -G is an anionic surface-active sulfate salt radical having the formula -OSO2-OR in which sulfate salt radical R is an alkyl group containing 10 to 18 carbon atoms, and wherein Z is a -COOM radical in which M is an alkali metal cation.
 23. The method of claim 16 wherein said imidazoline derivative is selected from the group consisting of 2-alkyl-1-(ethyl-betaoxypropanoic acid)-imidazolines wherein the alkyl group is selected from the class consisting of capryl, undecyl and mixtures of CC1, chains, and the disodium salt of lauroyl-cyclo-imidinium-1-ethoxyethanoic acid-2-ethanoic acid.
 24. The method of claim 16 wherein said imidazoline derivative is a mixture of (A) an imidazoline derivative wherein the groups -G and -CH2Z are both omitted and Y is -N((CH2)n-COOH)3C1, n being equal to 1 to 4; and (B) an imidazoline derivative wherein -G is -OH, wherein -Y is equal to -O(CH2)nCOOM and wherein Z is equal to -(CH2)mCOOM, n being equal to 1 to 4 and m equal to 0 to 1, and M being an alkali metal.
 25. The method of claim 24 wherein imidazoline derivative (A) is present in a weight ratio relative to imidazoline derivative (B) of about 1.0 to 8.0:1.0.
 26. The method of claim 16 wherein the alkyl group of said alkyl phenol in said condensate is selected from the class consisting of octyl, nonyl and mixtures thereof.
 27. The method of claim 16 wherein said carbinamine compound has the general formula and wherein e is an integer from 12 to
 15. 28. The method of claim 27 wherein in said carbinamine compound X is -H and a and b each represent numbers from 15 to
 20. 29. The method of claim 16 wherein said brightener has a heterocyclic ring and wherein an aldehyde group is attached directly to a carbon atom in the ring.
 30. The method of claim 29 wherein said heterocyclic ring contains five members.
 31. The method of claim 30 wherein said aldehyde brightener is thiophene aldehyde.
 32. The method of claim 16 wherein at least the predominant portion of said stannous ioN is provided by stannous sulfate and wherein a portion of said sulfate radical is furnished by sulfuric acid. 